This invention relates to a hydraulic power system for implement actuators in off-highway self-propelled work machines such as construction and industrial vehicles. The hydraulic power system according to the invention is particularly well suited for use in a motor grader or the like which requires operation of two or more implement actuators at the same time.
In a motor grader, for example, as it performs soil spreading, ditching and other duties usually assigned thereto, the need often arises for simultaneously effecting two or more of such implement operations as the shifting and swinging of the blade and the lifting or lowering of its lateral ends. The conventional implement control system in a motor grader has had several drawbacks. One of these is that when the opposite side ends of the blade are loaded to different degrees, they have been liable to be raised or lowered at different speeds. Also the revolving speed of the circle carrying the blade has been rather too low in some cases, resulting in unsatisfactory production. A further problem arises as when the vehicle is slowed down, and the implement assembly operated at the same time, to avoid its collision with some obstacle. The implement assembly has often been unable to clear the obstacle because its speed has decreased in step with reduction in engine speed.
An obvious remedy for all such inconveniences might be to employ hydraulic pumps of greater displacement. This measure, however, would inconveniently increase the operating speed of the blade and other implement actuators and thus adversely affect the performance of the machine. If the operating speed of the implement actuators were hydraulically reduced, then substantail waste of energy would result, and the hydraulic fluid and the actuators might overheat with operation for an extended length of time.